Development of slurry-based Ca sub 0.5 Sr sub 0.5 Zr sub 4 (PO sub 4 ) sub 6 (CS-50) coatings for SiC in fossil energy applications

• Published in: Materials at high temperatures 1999-01, Vol.16 (4), p.175-180
• Main Authors: Vaubert, V M, Janney, M A, Stinton, D P
• Format: Article
• Language: English
• ISSN: 0960-3409

Operating in a high temperature and highly corrosive environment requires the use of ceramic materials in many fossil energy applicatons. SiC-based materials are excellent candidates for these applications because they combine high strength and high thermal shock resistance at these temperatures. However, the corrosion of silicon-based materials in the presence of alkali species is a major problem. Coatings of Ca sub 0.5 Sr sub 0.5 Zr sub 4 (PO sub 4 ) sub 6 (CS-50), an ultra-low thermal-expansion material, have been successfully developed to protect SiC-based materials from sulfate salt corrosion. The coatings were applied to fiber-reinforced, SiC-matrix composite heat exchanger tubes and clay-bonded SiC. Aqueous slurries were prepared and applied to the SiC substrates. One coating process for heat exchanger material substrates, consisted of mechanically dipping the samples in a slip. A spin-coating process has also been developed that produced thin, non-obstructing coatings for hot-gas filter substrates. The thermal shock and corrosion resistance of coated parts were evaluated, and preliminary results are encouraging for the use of CS-50 as a protective coating. (Nicalon fiber reinforced SiC composites prepared by CVI.)